1. Field of the Invention
This invention relates to an automatic telecommunication switching center in which connections are set up in time division multiplex (TDM) manner and includes means functioning as a line scanner. The system includes auxiliary circuits to monitor code signals used, to detect codes, to convert one code to another, to adjust the speed between received and transmitted codes and/or to store and forward code signals.
2. Summary of the Invention
According to the invention there is provided an automatic telecommunication switching center, in which connections between communication channels are set up in TDM manner with each said channel allocated a time slot in the TDM cycle, in which the channels are all terminated at a storage array housing a storage compartment per channel served, in which each of said storage compartments has an "in" section and an "out" section, in which intelligence incoming to the center over one of the channels is recorded directly into that channel's "in" section, in which when a connection is set up between a first and a second channel each of these channels' "in" sections has recorded in it the storage address of the other of those channels plus the intelligence to be sent to that other channel, in which when the compartment for said first channel is scanned during said connection the intelligence in that channel's "out" section is read out to that channel and the contents of that first channel's "in" section is extracted and transferred to the second channel's "out" section under control of the address in that "in" section, in which the intelligence thus extracted from said first channel's "in" section is replaced by intelligence newly received from said first channel, in which when the compartment for said second channel is scanned during said connection the intelligence in that channel's "out" section is read out to the said second channel and the contents of that second channel's "in" section is extracted and transferred to the first channel's "out" section under control of the address in the second channel's "in" section, and in which the intelligence thus extracted from said second channel's "in" section is replaced by intelligence newly received from said second channel.
Further, the invention provides for the connection of an auxiliary circuit in parallel with the circuit between channels A and B, which auxiliary circuit may be used in various ways. For example, it may be used to connect a comparator into the system so that a particular code may be detected when it occurs in the normal transmission of information. Such a requirement is encountered in the case of data connections which are alternative to speech connections, so that a connection may be set up in the speech mode, but may be terminated in the data mode by some form of coded signal. In this case a monitor detects the presence of such an end signal and clears the connection accordingly.
Another application is to the conversion of the code which might be received in one variety and transmitted in another, while retaining the same basic character rate. In this case the information is not directly connected through from A to B and vice versa, but via the auxiliary circuit and through the auxiliary circuit into the code converter and back with the converted code to the direction concerned.
Similarly, in the case of code conversion involving a speed change or for store and forward facilities where storage is involved, the system can carry out a similar function to that outlined for code conversion, the information received on channel A being transferred via the auxiliary circuit to the appropriate converter-speed changer and retransmitted from the converter in the appropriate direction. The intelligence is handled in a delta modulation form, which is a variant of PCM in which intelligence is sent to each time slot as a bit of one polarity or a bit of the opposite polarity, depending upon whether the signal is increasing or decreasing. However, the invention can equally be used where the intelligence handled is in conventional PCM or other forms of coding.